Known as a conventional technique in the field mentioned above is a wafer dividing method comprising the steps of irradiating a wafer with laser light, which is transmissible through the wafer, along a line to divide, so as to form a modified layer within the wafer along the line to divide; and then expanding an expandable protective tape attached to one surface of the wafer, so as to divide the wafer along the modified layer (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-129607